The present invention relates to telemetering systems designed to transmit information from the bottom of a borehole to the surface while drilling a well. In the rotary drilling method, a string of pipe, having a drill bit at its lower end, is rotated to drill the well while circulating fluid down the drill pipe and up through the annular space between the drill pipe and the borehole. The circulating fluid is used to carry the drill bit cuttings to the surface and clean out the borehole. While the most common type of rotary drilling uses a drill rig to rotate the drill string, the invention may also be used when a mud turbine is used to rotate the drill bit.
One of the prior art systems used to telemeter information while drilling relies upon the production of pressure pulses in the mud stream to telemeter information to the surface. Additional systems, relying upon introduction of a wireline from the surface to the bottom of the borehole, have been used to transmit information to the surface. Likewise, various systems have been developed for installing the wireline in the drill string. For example in U.S. Pat. No. 3,696,332, there is disclosed a specialized drill string in which an insulated conductor is positioned in each section of the drill string and coupled to suitable ring-like connectors disposed in the sealing shoulders of each section of the drill string. In addition, the patent discloses using a single wireline to span a portion of the drill string, and the specialized drill string to complete the circuit between the end of the wireline and the surface of the well. This permits deepening the well while adding additional sections of the specialized drill string and still maintaining an electrical circuit to the bottom of the well. The advantage of using a wireline to span a portion of the drill string is a reduced cost since less of the specialized drill string and a reduced number of electrical connectors will be required.
While the above patent discloses a combination system, it relies on conventional wireline equipment for installing the continuous wireline in a portion of the drill string. While this is satisfactory, it is preferable to have specialized equipment for installing and removing the wireline. In particular, it is desireable to have a releasable connector on the bottom of the wireline for connecting the wireline to the bottom hole instrument package. In addition, some means is required for anchoring the top of the wireline so that it can be tensioned to avoid slack in the wireline. It is also desirable that the complete wireline and associated equipment be removable from the drill string to permit the introduction of additional wireline tools from the surface, or the use of fishing equipment to recover instruments introduced from the surface, or the use of fishing equipment to recover instruments introduced into the drill string. When the wireline is removed, the drill string should be clear of restrictions.